What Is Switch Virtualization Technology and What Are Stacking and M-LAG, What Are Their Differences
This document describes the concepts of stacking and Multichassis Link Aggregation Group (M-LAG), their functions on the network, as well as their differences.
This document describes the concepts of stacking and Multichassis Link Aggregation Group (M-LAG), their functions on the network, as well as their differences.
What Is Switch Virtualization Technology & What Are Stacking and M-LAG, What Are Their Differences
Overview
With the switch virtualization technology, multiple physically connected switches can be logically integrated to increase the bandwidth of virtual switches and improve forwarding efficiency. A physical switch can be logically virtualized into multiple virtual switches to isolate services and improve reliability.
Stacking and M-LAG are widely used among these technologies. They are often used to improve the reliability of access devices. What are their differences? What advantages do they have? How can you select a proper one between them? You will find the answers in this document.
What Are Stacking and M-LAG?
Stacking and M-LAG are switch virtualization technologies that improve reliability, expand bandwidth, and implement load balancing.
What Is Stacking and What Are Its Functions?
Definition of Stacking
As shown in Figure 1-1, multiple switches are connected through stack cables and are virtualized into a logical switch through the stacking function. The logical switch appears as one switch for data forwarding.
Functions of stacking
- Increasing the number of ports
As shown in Figure 1-2, when the port density of a switch is insufficient for an increasing number of users, you can connect another switch to the switch using stack cables, and configure them to set up a stack to provide more ports.
- Expanding bandwidth
As shown in Figure 1-3, when higher uplink bandwidth is required, a new switch can be added to form a stack with the existing switch, and their physical links can be bundled into a link aggregation group to expand the uplink bandwidth.
- Enhancing reliability
As shown in Figure 1-4, stacking and Eth-Trunk are used together. When the uplink of a switch in the stack fails, traffic passing through the switch can be forwarded through the iStack link.
What Is M-LAG and What Are Its Functions?
Definition of M-LAG
M-LAG implements link aggregation among multiple devices. As shown in Figure 1-5, two switches are connected through a peer-link and they negotiate link aggregation with their connected host in the same state. This improves link reliability from the card level to the device level.
Functions of M-LAG
- Balancing load
As shown in Figure 1-6, an access device is dual-homed to two M-LAG member devices in an M-LAG dual-active system through an Eth-Trunk. After receiving the access device's traffic that is load balanced through bundled links, both the two M-LAG member devices forward the traffic.
- Enhancing reliability
As shown in Figure 1-7, devices are connected to the Ethernet using an M-LAG. When the uplink of the M-LAG master device fails, traffic passing through the M-LAG master device is forwarded by the M-LAG backup device through the peer-link.
Differences Between Stacking and M-LAG
Although both stacking and M-LAG improve reliability by virtualizing multiple devices into one device, their configurations vary significantly, including the dual-active detection (DAD) mode, status negotiation mode, virtual system IP address, and virtual system MAC address. Table1 lists the differences between stacking and M-LAG.
Item |
Stacking |
M-LAG |
|---|---|---|
Virtual system IP address |
One IP address is provided for all stack members. After a stack takes effect, each member's own IP address becomes invalid. |
M-LAG members have their own IP addresses. No unified IP address is available for all M-LAG members. |
Virtual system MAC address |
One MAC address is provided for all stack members. After a stack takes effect, each member's own MAC address becomes invalid. |
M-LAG members have their own MAC addresses. No unified MAC address is available for all M-LAG members. |
Device login |
Logging in to any device in the stack is equivalent to logging in to the master device. |
All devices are independent of each other, and each device has an independent management port. |
DAD link |
|
Layer 3 reachable link |
Status negotiation |
Packets are transmitted over the iStack link. |
Hello packets and packets carrying device information are transmitted over the peer-link. |
Detectable faults |
|
|
Advantages and Disadvantages of Stacking and M-LAG
The configuration of stacking differs greatly from that of M-LAG, and each has its own advantages, as listed in Table1.
Item |
Stacking |
M-LAG |
|---|---|---|
Reliability |
Average: The control plane is centralized, and faults may be spread on stack members. The failure of the master switch may affect other stack members, and the reliability is low. |
Relatively high: Control planes are independent and the fault domain is isolated. |
Cost |
Average: Stack cables need to be deployed. |
Average: Peer-link cables need to be deployed. |
Configuration complexity |
Simple: Multiple devices are configured at the same time and logically virtualized into one device. |
Average: Multiple devices are configured independently. |
Scalability |
Average: The control plane's capabilities rely on the master switch. |
Relatively strong: The scalability is not restricted by a single device. |
Impacts on services |
Upgrade: Services are interrupted for 20 seconds to 1 minute. Capacity expansion: When capacity expansion is performed for a stack with three or more devices, the original network architecture needs to be changed or the devices need to be restarted, affecting existing services. |
Upgrade: Traffic is interrupted for seconds. Capacity expansion: The original network architecture is not changed, and the existing services are not affected. |
Upgrade complexity |
High: Fast stack upgrade reduces the service interruption time but increases the upgrade operation time and upgrade risk. |
Low: The upgrade is performed by restarting the device, which is simple and of low risk. |
Network design |
Relatively simple: Single-node design is used logically. |
Relatively complex: Dual-node design is used logically. |
To sum up, stacking is easier to configure and design than M-LAG, but is less flexible, less reliable, and more complex to upgrade. Although more complex to configure, M-LAG has higher reliability than stacking due to decoupling of the control plane and high networking flexibility.
Related Information
For details about how to configure stacking and M-LAG, see the configuration manual of each product at Huawei technical support website.
For details about M-LAG, see What Is M-LAG and M-LAG Best Practices.
For details about how to switch from a stack to an M-LAG, see How Do I Switch from a Stack to an M-LAG.